1. Field of the Invention
The present invention relates to fuel injectors, and more particularly, to a feed arm for a multiple circuit fuel injector of a gas turbine engine.
2. Description of Related Art
Fuel injectors in gas turbine engines direct pressurized fuel from a manifold into one or more combustion chambers. Fuel injectors also function to prepare the fuel for mixing with air prior to combustion. Each injector typically includes an inlet near the manifold, one or more tubular fuel passages, and an outlet connected to a spray nozzle for introducing atomized fuel into a combustion chamber. The atomized fuel is then typically mixed with air and ignited, and the resulting expanded gas causes a plurality of turbine blades to rotate, thus providing power for propelling an aircraft or for other applications.
Many fuel injectors include multiple fuel flow passages, allowing for the power output of the gas turbine engine to be more easily adjusted. For example, a fuel injector may have a primary fuel flow passage and a secondary fuel flow passage, with both passages being used during higher power operation and only the primary fuel flow passage being used during lower power operation.
Fuel injectors also typically include heat shields surrounding the tubular fuel passages to protect the fuel flowing through the passages from the extreme heat generated in the combustion chamber. These heat shields are necessary to prevent coking, the breaking down of the liquid fuel into solid deposits. Coking is likely to occur when the temperature of the wetted walls in a fuel passage exceeds a maximum value. When coking occurs, solid deposits can form within the fuel flow passage, which restricts the flow of fuel through the passage and can render the fuel injector ineffective or unusable.
Conventional multiple circuit fuel injectors include a tubular member with primary and secondary fuel flow passages. The primary fuel flow passage is formed through a central portion of the tubular member, and the secondary fuel flow passage is formed surrounding the primary fuel flow passage. Fuel flows continuously through the primary fuel flow passage, however fuel may flow only intermittently through the secondary fuel flow passage. Depending on the operational requirements of the engine, the velocity of the fuel flow through the secondary passage may be decreased, or the flow may be stopped altogether. As a result, stagnate fuel may be present in the secondary fuel flow passage. Because the secondary fuel flow passage has a reduced fuel velocity, and because the secondary fuel flow passage is in close proximity to the extreme heat generated by the combustion chamber, coking of the fuel within the secondary fuel flow passage is a common problem.
Thus, there is a need for improved methods and systems for preventing coking in both primary and secondary fuel flow passages of fuel injectors for gas turbine engines.